Chlorofluoroethanes
		Chlorine
	Nuclear Quadrupole Coupling Constants
		in the Chlorofluoroethanes
	The summary given here is of nqcc's in the principal axes of the nqcc tensor calculated on ab initio molecular structures, corrected as discussed below.
	Table 1. 35Cl nqcc's in the Chlorofluoroethanes (MHz).   First row, calculated nqcc's using B3P86/6-311+G(3d,3p) angles; second row, MP2/6-311+G(d,p) angles (see below).   ETA = (Xxx- Xyy)/Xzz Øz,CCl is the angle between the principal z-axis and the CCl bond axis.   Molecule Xzz Xyy Xxx ETA Øz,CCl     H2ClC-CH3 -71.00 35.85 35.15 0.010  0.61 -71.22 35.83 35.39 0.006  0.96   t-H2ClC-CH2F -73.39 37.83 35.56 0.031  0.03 -73.58 37.86 35.72 0.029  0.25   H2ClC-CHF2 -77.22 39.80 37.41 0.031  0.91 -77.44 39.80 37.64 0.028  0.95   H2ClC-CF3 -78.51 40.67 37.84 0.036  0.75 -78.66 40.63 38.03 0.033  0.42   F2ClC-CH3 -72.14 35.46 36.68 - 0.017  0.48 -72.31 35.50 36.81 - 0.018  0.24   F2ClC-CH2F -72.13 36.82 35.31 0.021  0.81 -72.31 36.87 35.44 0.020  0.67   F2ClC-CHF2 -75.77 38.16 37.61 0.007  1.47 -75.88 38.16 37.72 0.006  1.24   F2ClC-CF3 -76.69 38.74 37.95 0.010  1.51   -76.76 38.68 38.07 0.008  1.24
	Table 2.  Xzz (MHz).  CCl and CC Bond Lengths (Å).   Xzz CCl CC   H2ClC-CH3 -71.00 1.7864 1.509   -71.22   H2ClC-CH2F -73.39 1.7764 1.508 -73.58   H2ClC-CHF2 -77.22 1.7642 1.504   -77.44   H2ClC-CF3 -78.51 1.7596 1.505 -78.66   F2ClC-CH3 -72.14 1.7686 1.496   -72.31   F2ClC-CH2F -72.13 1.7624 1.508 -72.31   F2ClC-CHF2 -75.77 1.7394 1.525 -75.88   F2ClC-CF3 -76.69 1.7409 1.536 -76.76
	Molecular Structure
	The molecular structures were optimized at the MP2/6-311+G(d,p) level of theory assuming Cs symmetry.  The optimized CC single bond length was then corrected using the equation obtained from linear regression analysis of the data given in Table IX of Ref.[3].  Likewise, the optimized CF bond lengths were corrected by regression analysis of the data given in Table VI of Ref.[2].  For the CCl bond, the structure was optimized at the MP2/6-311+G(2d,p) level and corrected by linear regression analysis of the data given in Table 4 of Ref.[1].  The CH bond lengths were corrected using r = 1.001 ropt, where ropt is obtained by MP2/6-31G(d,p) optimization [4].  Interatomic angles used in the calculation are those given by B3P86/6-311+G(3d,3p) optimization, and by MP2/6-311+G(d,p) optimization.
	Comment
	For the H2ClC-CHnF3-n ethanes, there is a good linear relationship between the Xzz and the inverse cube of the CCl bond lengths.  For calculation made with the B3P86 and MP2 angles respectively, linear regression analyses give correlation coefficients of 0.9985 and 0.9983, and residual standard deviations of 0.23 and 0.25 MHz. Such is not the case for the F2ClC-CHnF3-n ethanes.
	Figure 1 (PDF) is a plot of Xzz vs inverse cube of CCl bond length for the case where the interatomic angles are those given by B3P86/6-311+G(3d,3p) optimization.
	[1] I.Merke, L.Poteau, G.Wlodarczak, A.Bouddou, and J.Demaison, J.Mol.Spectrosc. 177,232(1996).
	[2] R.M.Villamañan, W.D.Chen, G.Wlodarczak, J.Demaison, A.G.Lesarri, J.C.López, and J.L.Alonso, J.Mol.Spectrosc. 171,223 (1995).
	[3] J.Demaison, J.Cosléou, R.Bocquet, and A.G.Lesarri, J.Mol. Spectrosc. 167,400(1994).
	[4] J.Demaison and G.Wlodarczak, Structural Chem. 5,57(1994).
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	Molecules/Chlorine
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						Last modified 14 Aug 2004